This invention relates to an optical switch apparatus.
It is often required to switch light from one port to another. For example, in the field of telecommunications, data may be carried as optical data in an optical beam, and in order to process the optical data, it is often necessary to switch the optical beam from one waveguide to another.
Optical switches are known in which light is transferred from one waveguide to another, not by means of a mechanically moveable member, but by causing light to couple directly from one waveguide to the other through the walls of the waveguide over a distance known as the coupling length. In a known example of an optical switch apparatus of this kind, the waveguides take the form of elongate channels having a predetermined refractive index which are formed in or on a body of lower refractive index. When light enters the first waveguide, some of the light is coupled from the first waveguide to the second waveguide and emerges from the second waveguide. Thus there is some degree of optical coupling between the two waveguides. However, it is often desired either to have all the light which entered the first waveguide emerge from the first waveguide, this condition being known as the "through state" of the switch, or to cause all the light which entered the first waveguide to be coupled to the second waveguide and emerge from the second waveguide, this being known as the "cross state" of the switch. Application of a suitable electric field to the body modifies the degree of optical coupling which occurs between the two channels by altering the refractive index of the channels due to the electro-optic effect. By correctly choosing the electric field in relation to the optical properties of the switch, light is caused to largely transfer from one channel to the other. The transfer of light is, however, not complete and both the through state and the cross state are difficult to achieve in a reliable manner as a number of difficult design constraints have to be satisfied.